One should not work Prussian blue into one’s drawing of a face; for then it ceases to be flesh and becomes wood.
–Vincent Van Gogh
Prussian blue — the shade is like the ocean somewhere between sun-soaked aqua and deep black waters, or like opal in shadow. The hue is named after the uniforms worn by the eponymous Germanic state’s military. That is, the ones they wore in the 18th century through the Napoleonic and Franco-Prussian wars. During World War I, the Germans replaced Prussia’s blue regalia with feldgrau, a greenish gray more suited (pun intended) to the war machine. Sapphire was too precious for that scale of bloodshed, so exponentially greater than the previous centuries’ continental battles when the French, too, wore blue. Apparently, friendly fire was not so great a risk before machine guns and weaponized aircraft.
The uniforms’ blue shade was synthesized accidentally in German scientist Johann Dippel’s laboratory. Having failed to alchemize gold, Dippel sought to create a universal medicine with a substance called “animal oil,” animal blood mixed with potassium salts. In 1705 (some sources say 1704 or 1706), he was sharing his lab with the colourist Diesbach. Diesbach accidentally added animal blood-contaminated potassium salt to the scarlet dye he was working with. Red plus red equals blue.
Where Dippel failed in creating a cure for every ailment from the substances in his laboratory, modern medicine has succeeded for one. Prussian blue is an effective antidote for heavy metal poisoning by the elements thallium and cesium. The radioactive compounds travel through the liver, posing danger of absorption when they reach the small intestines. But if you swallow a pill of Prussian blue, the ingested molecules will trap the harmful micro-droplets and prevent them from being absorbed into the blood. Instead, the blue ferries them out in a bowel movement.
Our bodies simply cannot absorb tiny beads of blue. A food-coloured bagel I once had tasted more of dye than the blueberry it represented. Though I ate only half, my mouth turned blue. Days later, so did…bear with me here…my excrement. It seems that being “blue” can only describe our emotional mire, not anything corporeal. The colour exists exteriorly, outside of our body’s compounds. Unlike the brown-black melanins, dark-brown lipochromes, yellow-orange carotenes that are naturally present and soluble in our bodies. Unlike crimson liquid seeping into a Prussian uniform.
In WWII, the Germans employed Prussian blue for new sartorial uses. Spies wrote secret words on their socks and cloth buttons. When sprayed with ferrocynaide, letters scrawled in ferric sulfate revealed themselves in blue lines upon the fibres. For less nefarious messages, Prussian blue was used in 1847, on two pence stamps for Britain’s Mauritius island colony. Now, those few remaining postage pieces are valued around £2,000,000. Jewel-toned indeed. Japan, too, used Prussian blue—though in art, not war. The pigment came to Asia by way of an entrepreneur in Guangzhou, China in the 1820s, and the colour was so prolific among Japanese print-making that it is said to have inspired the pure landscape genre ukiyo-e. The blue propels white claw-capped waves in Katsushika Hokusai’s Great Wave (1830), driving them ever east.
In an exhaustive study of ancient texts—in Icelandic, Chinese, Vedic, Hebrew—philosopher Lazarus Geiger searched unsuccessfully for a blue word. In a close read of the Iliad and the Odyssey, British Prime Minister William Gladstone found an equal lack of blue. Black appeared around 170 times. White, 100. Red, 13. Yellow, less than ten. Green, less than ten. Blue? Not once. Modern day linguist Guy Deutscher reasons that languages had no need for a colour’s word until it could be manufactured by human hands. Red, easily pulled from earth’s clay, appears in language first. Blue, finicky and rare in nature, was always last. Rare in nature—except for the vast swath above. Geiger wrote of Indian Vedic poems, “these hymns of more than 10,000 lines are brimming with descriptions of the heavens. Scarcely is there any subject evoked more frequently…There’s only one thing that no one would ever learn from those ancient songs who do not already know it. That the sky is blue.”
Blue had been part of Europe’s languages far before Dippel and Diesbach’s happy accident. But Prussian blue was one of the first colour-stable azure dyes. On that continent in that century, when religious motifs dominated painted canvases, Prussian blue’s discovery may have been the perfect opportunity to capture the cerulean kaleidoscope sky and its zenithal heavens beyond. Before, it was best preserved in words and in faith. Why not capture the divine eternal in blue brushstrokes? Yet, painting’s first recorded use of Prussian blue is Pieter van der Werff’s Entombement of Christ (1709). Van der Werff did not dip his bristles in deep blue for the celestial above. Nor does the painting’s holy subject, the martyr, model the colour. Instead, van der Werff used the pigment for one of the group surrounding Christ. If the son of God were to open his eyes, he would see blue—but not of the heavens. On a shrouded figure, Prussian blue robes divinity’s opposite: a mortal man, for centuries to come.